Just for comparison the actual values are like this:

AWG___mm&#178

4/0__107
3/0__85.0
2/0__67.4
1/0__53.5
1____42.4
2____33.6
3____27.0
4____21.2
5____16.8
6____13.3
7____10.6
8____8.35
9____6.62
10___5.27
11___4.15
12___3.31
13___2.63
12___2.08
15___1.65
16___1.31
17___1.04
18___0.823
19___0.653
20___0.519
21___0.412
22___0.325
23___0.259
24___0.205
25___0.163
26___0.128
27___0.102
28___0.0804
29___0.0646
30___0.0503

As you can see, the difference is significant only for sizes 0 and larger.

At the same time, anyone familiar with metric sizes will object. Quite correctly: The last few sizes in the first message don't exist. For some reason the sizes leave logic after 25mm&#178. Instead of 40 like you would expect, they have choosen 35. And this then goes on with illogical sizes like 95mm&#178. The whole thing should be reworked.

Here's the MCM to actual metric to my suggested 'rough' conversion. Why are there so many MCM sizes? You can't possibly stock them all.

2000___1013____1000mm&#178
1750___887_____Remove size
1600___809_____800mm&#178
1500___760_____Remove size
1250___633_____630mm&#178
1000___507_____500mm&#178
800____405_____400mm&#178
750____380_____Remove size
700____355_____Remove size
600____304_____315 mm&#178
500____253_____250 mm&#178
450____228_____Remove size
400____203_____200 mm&#178
350____177_____Remove size
300____152_____160 mm&#178
250____127_____125 mm&#178

Look at the numbers and you'll see that the conversion is rather simple...